And he says that a win would help him claim the Republican presidential nomination "well before" his party's national convention in August.

Speaking to voters inside a call center for Republican governor Scott Walker on Saturday afternoon, Romney says that support for his campaign "is growing stronger and stronger." He says it looks like he's going to win the Wisconsin contest and could win the other two elections on Tuesday in Maryland and the District of Columbia.

With Wisconsin Congressman Paul Ryan at his side, Romney says that winning all three would be "a big statement."